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This paper studies the effect of graphene oxide (GO) on the strength and interface transition zone of recycled aggregate concrete (RAC). The results show that the addition of GO enhances the RAC strength, and the compressive strength of the sample containing GO is improved by 7% ~ 20.6% at 28 days, compared with the reference group. Meanwhile, with the addition of GO, the total porosity and the number of harmful pores (> 100 nm) of RAC samples decreased by 8.1% ~ 35.7% and 3% ~ 39.1%, respectively. It is observed from the nano scale characteristics that the addition of GO can significantly reduce pore phase and unhydrated phase content in the matrix, and increase the volume fraction of C-S-H phase, especially the high-density C-S-H phase. In addition, the width of the interface transition zone between old mortar and new mortar containing GO sample is relatively reduced by 25%, but there is no obvious change in the interface transition zone of old aggregate mortar. The strengthening effect of GO on RAC strength is due to the nucleation of GO and the filling effect of micro-aggregate, improving the pore structure and interface transition zone of RAC.

Foamed porous cement materials were fabricated with H2O2 as foaming agent. The effect of H2O2 dosage on the multifunctional performance is analyzed. The result shows that the obtained specimen with 0.6% H2O2 of the ordinary Portland cement mass (PC0.6) has appropriate porosity, leading to outstanding multifunctional property. The ionic conductivity is 29.07 mS cm−1 and the compressive strength is 19.6 MPa. Furthermore, the electrochemical energy storage performance is studied in novel ways. The PC0.6 also shows the highest areal capacitance of 178.28 mF cm−2 and remarkable cycle stability with 90.67% of initial capacitance after 2000 cycles at a current density of 0.1 mA cm−2. The superior electrochemical energy storage property may be attributed to the high porosity of foamed cement, which enlarges the contact area with the electrode and provides a rich ion transport channel. This report on cement–matrix materials is of great significance for large scale civil engineering application.